This week Facebook users across the nation have been having a heart attack and grabbing their tinfoil hats in horror over what they saw as an almost science-fiction-like Facebook feature they believed to have just crept up on them to grab them in the night: a list of phone numbers. As you may or may not know, Facebook has had your phone number ever since you first entered it in when you signed up for the site. Didn't sign with your phone number in the first place? Did you download a Facebook app of basically any kind on any sort of smartphone in the past? If you did, you agreed to have your mobile phone number shared with all of your friends.
The only thing relatively new is the actual list of phone numbers. These numbers have been available to you and your friends for many months now, but only in the past few days has the torrent of REALIZATION come forth. You may have seen a message (or a derivation in one way or another) such as this permeate your Facebook news feed:
This is true! ALL THE PHONE NUMBERS of ur contacts are now on facebook! Go to the top right of the screen, click on ACCOUNT, click on EDIT FRIENDS, left side of screen and click CONTACTS. You will see ALL PHONE NUMBERS FROM YOUR CELL PHONE (FB friends or not) have been published. To remove, go to the right column below Phonebook Contacts, and click on "THIS PAGE." Please repost this on your status, so your friends can remove their numbers and thus prevent abuse if they do not want them published!
If you do take heed and follow the directions from the crazy person above, you'll actually be removing the contacts you've imported from your mobile device, or so Facebook would have you believe. You'll also have to go through a process (as seen in the picture below) where you hit up your Facebook app and switch off Syncing. The directions here direct you to do so with your iPhone app, but a similar process works for Android.
This big list of numbers you've seen isn't public, or isn't any more public than each of the numbers is on its own - if your friend has a profile with a publicly displayed phone number, it's going to be public regardless of what YOU do. Again note that these numbers come from Facebook, not your unconnected contacts book, certainly not if your contacts aren't connected to Facebook. Also you might want to know that if you've ever typed your phone number anywhere on Facebook, it's accessible, as the classic Tom Scott webpage "EVIL" shows quite clearly.
In summation: the numbers come from the users who have entered them themselves. No Facebook user that you didn't allow the ability to see your number has access to your number. Keep yourself the safest by not entering the information you want kept secret by not posting it on the internet in the first place.